The invention relates to a shaft rotating device for rotating a shaft of a medical instrument about its longitudinal axis relative to a handle of the medical instrument.
The invention further relates to a medical instrument for endoscopic surgery, comprising a shaft and a handle, wherein the handle is arranged at a proximal portion of the shaft.
A shaft rotating device and a medical instrument are known from EP 2 077 094 A1.
The known medical instrument comprises an elongated shaft, at whose proximal portion a handle is arranged. A distal portion of the shaft is used to introduce pivotably arranged jaws into a cavity of a patient during an operation for grasping and/or cutting tissue. At least one jaw is in driving connection with the handle via a thin pull/push rod for controlling its grasping and/or cutting action. At the proximal portion of the shaft a shaft rotating device is arranged, which allows for rotating the shaft about its longitudinal axis relative to the handle and against frictional forces exerted between a surface of a frictional element comprising two coil springs wound counter-directionally around a surface of a counterpart which is connected with the handle.
This arrangement of the frictional element on the one hand and the counterpart on the other hand provides the frictional forces, such that the shaft and the handle are rotationally stationary with respect to each other, when no forces are applied to the operating element. In addition, when applying a torque to the operating element, the frictional forces are decreased such that the shaft is easily rotatable relative to the handle without increased physical effort. In contrast, applying a torque to the distal portion of the shaft results in an increase of the frictional forces such that the shaft and the handle are rotationally fixed to each other. Thereby, it is ensured that the jaw parts do not change their rotational orientation when torques are exerted on the jaw parts during the grasping and/or cutting action.
In the known shaft rotating device, two coil springs wound counter-directionally with respect to one another are used to achieve both, a decrease of the frictional forces when a torque is applied to the operating element and an increase of frictional forces when a torque is applied to the distal portion of the shaft.
Thus, the known shaft rotating device has the drawback, that the frictional element, comprising two coil springs which require relatively large space, is complex and cost intensive in terms of manufacturing expenditure.
Furthermore, it is a disadvantage that a rotation transmission element of the shaft rotating device which is arranged between the operating element and the coil spring arrangement, comprises a complex arrangement of at least three separated grooves in which the end portions of the two counter-directionally wound coil springs engage. This complex design also causes an increased effort during manufacturing accompanied by increased production costs and increased effort in assembling and disassembling the device.